It is known to provide a fuel tank in a vehicle to hold fuel to be used by an engine of the vehicle. It is also known to provide a fuel sensor or indicator in the fuel tank to indicate the level of liquid fuel in the fuel tank. Typically, the fuel indicator includes a variable resistor operatively connected to structure of a fuel delivery module and a wiper assembly pivotally connected to the structure for engaging the variable resistor. The wiper assembly has one end connected to a float to rotate the wiper assembly relative to the variable resistor based on a level of liquid fuel in the fuel tank.
Typically, the fuel indicators are analog devices that measure liquid fuel height or fuel level through a position change by a float arm that is connected to the fuel indicator. The position change is a change in resistive measurement by the fuel indicator to indicate a change in the fuel level. However, the sliding contacts of the fuel indicator are impacted with changes in the fuel. The impact of the various chemicals within the fuel can cause contact resistance that translates into a “signal noise” or open contacts. Since the composition of fuel is constantly changing, it is desirable to eliminate sliding contacts exposed to fuel for the fuel indicator. A number of technologies exist which eliminate sliding contacts. These technologies include inductance and Hall effect sensors. However, it is also desirable to eliminate float arms or other moving parts of the fuel indicator.
To eliminate moving parts, the selection of technologies is limited to capacitance, optics, force gages (weight), and sonics (piezo electric). All of these technologies have disadvantages in indicating all of the available fuel due to various configurations of the fuel tanks, as well as to the unique environment presented by fuels consisting of “gasoline” and alcohols, both in liquid and vapor stage. For capacitance, the fuel indicator is affected by the conductivity of the fuel, stratification of the fuel, the coating of the capacitance element by organic and inorganic compounds, and the need to have electronics associated with the fuel indicator in close proximity thereto, i.e. inside the fuel tank. For fiber optics, the fiber optics in either the form of fiber optic strands or light pipes are affected by the variations in color of the fuel and by the tendency of the fiber optic or light pipe element to become coated with organic and inorganic compounds. For force/strain gage (weight), as the level of liquid fuel drops toward empty, the resolution becomes less and less until a point is reached where there is insufficient mass to produce a signal. For sonics, piezo electric crystals are normally positioned in close proximity to a bottom of the fuel tank since dynamic ranges of the crystals are such that the sonics created are more effective in liquid as compared to air. The piezo electric crystals provide good accuracy with the exception of a zone directly above the crystals, which is referred to as the “dead” zone. This zone is approximately 15 millimeters (mm) above the crystals where the crystals are unable to differentiate sufficiently between the emitted and received signals. In addition, stratification of alcohol blended fuels may impact the accuracy of the indicated fuel level.
All of the above-described technologies, without moving parts, are difficult to package within the fuel tank. It is also desirable to minimize the openings into the fuel tank to reduce fuel permeation, thus the fuel level device is normally assembled as part of the fuel delivery module. Depending on the location of the tank opening, these devices may not be able to indicate fuel levels higher than the location of the fuel delivery module permits.
Therefore, it is desirable to provide a fuel level indicator that eliminates sliding contacts exposed to fuel. It is also desirable to provide a fuel level indicator that eliminates moving parts. It is further desirable to provide a fuel level indicator that has a relatively low cost.